Chap, iv.] METABOLIC PKOCESSES OF THE BODY. 585 



times called haematoporphyrin) is said to have the composition 

 C 3 ,H 39 N 4 5 , differing from bilirubin only in its oxygen and 

 hydrogen (C 32 H 32 N 4 5 + 2H 2 - O = C^N^). 1 Moreover 

 in old blood clots in the body the haemoglobin of the clot becomes 

 in time transformed into an iron-free body which has been called 

 hsematoidin, but which both in composition and in reactions 

 appears to be identical with bilirubin. 



These several facts lead us to the conclusion that the biliru- 

 bin of the bile is simply some of the haemoglobin of the blood 

 transformed by the throwing off of its proteid and its iron com- 

 ponents. It is natural to suppose that the transformation takes 

 place in and is effected by the agency of the hepatic cells ; and 

 this view is supported by the fact that the hepatic cells are 

 characterized by containing certain peculiar iron compounds. 

 When all the blood is carefully washed out of the liver by injec- 

 tion through the blood vessels, by which means the remaining 

 bile is got rid of at the same time, the hepatic substance is found 

 to contain a small quantity of iron, sufficient to give the cells 

 a diffused dark colour when treated with ammonium sulphide ; 

 the exact amount appears to vary largely, but the causes of the 

 variation have not been determined. That this iron is in organic 

 combination is indicated by the fact that with potassium ferro- 

 cyanide and sulphocyanide the blue or red reaction is not 

 observed until after treatment with hydrochloric acid. Appar- 

 ently there are several such compounds, of a proteid or of a 

 nuclein (§ 29) nature, from some of which the iron is more 

 easily removed than others, and these compounds appear to be 

 present in both the cell-substance and the nucleus. It will be 

 remembered (§ 205) that bile contains a distinct quantity of 

 iron, which probably has its origin in the iron thus set free from 

 haemoglobin and retained in the hepatic cell ; but it does not 

 follow that all the iron thus set free makes its way into the 

 bile ; and indeed the quantity of iron discharged in the bile in 

 24 hours is much smaller than the quantity calculated to be set 

 free in the formation out of haemoglobin of the quantity of bili- 

 rubin discharged during the same period. Apparently the iron 

 compounds of the hepatic cell have some other work than the 

 simple discharge of iron into the bile. 



§ 376. We may assume then that the hepatic cell has the 

 power of splitting up the haemoglobin brought to it, and of 

 discharging part as bilirubin while it retains for a time the iron 

 component in some organic combination. But are we justified 

 in assuming that the whole work is done by the hepatic cells ? 

 Are we to conclude that bilirubin is manufactured by some 

 act of the hepatic cells which includes not only the conversion 

 of haemoglobin into bilirubin, but also the extraction of the 



1 Doubling the formula for bilirubin given in § 206. 



